Abstract
A detailed study of the surface modification of PVdF by alkaline treatment at 80°C, has been carried out by X-ray photoelectron spectroscopy, secondary ion mass spectrometry, Raman spectroscopy, infrared spectroscopy and Rutherford backscattering spectrometry. The surface composition of the modified polymer has been shown to consist of conjugated polyene sequences, oxygen species and some fluorine containing groups. The reaction is essentially defluorination, followed by oxygenation. The oxygen species created are in the form of hydroxyl, carbonyl and O-C-F groups. The fluorine is shown to remain in the polymer in the form of =CF groups and O-C-F species, and in some cases a small amount of CF2 groups. Three different types of media have been used to treat the PVdF samples, 12 M sodium hydroxide, 4 M sodium hydroxide with the addition of phase transfer catalysts (PTCs), and 4 M sodium hydroxide with addition of the solvent dimethyl sulphoxide (DMSO). A combination of the DMSO and PTC treatments have also been investigated. The main PTCs used in this research are tetrabutyl ammonium hydrogen sulphate (TBAHS) and tetrabutyl phosphonium bromide (TBPB). The proposed mechanism does not alter for the different treatments described above, however the surface composition does differ slightly. This is a result of changes in the process kinetics with the reagents employed. In the case of the 12M NaOH, the first step, deprotonation, is rate- controlling, therefore intermediates which are observed in the other treatments, which do not have a well-defined rate-controlling step, are not observed in this case. The kinetics of the reaction mechanism not only affects the observed surface composition, but also the depth of treatment. The depth of treatment in this work spans a range from <0.1 μm (12 M NaOH) to approximately 2 μm in the case of the DMSO treatment. Thus the kinetics of the reaction, and depth of defluorination is increased by the addition of either PTC or DMSO to the alkaline solution. The DMSO has a greater effect on both parameters than the PTC.